Method of making coil for absorption refrigeration apparatus



1957 a. R. REISTAD 3,348,4Q2

METHOD OF MAKING 0011, FOR ABSORPTION REFRIGERATION APPARATUS FiledMarch 27, 1964 5 $heets-$heet 1 INV TOR hl rraeA/a Oct. 24,1967 a. R.nus-mp 7 3,358, 02. I usraob b? MAKING 00 11. FOR ABSORPTIONnnrnmnmnqfifA PI Q N IUS' I I Filed March 27;. 19 e4 INv ziNToR-p j- 2 1967 B. R.REISTAD 3,348,402.

METHOD OF MAKING COIL FOR ABSORPTION REFRIGERATION APPARATUS Filed March27, 1964 5 Sheets-Sheet 5 I NVENTOR.

W/ WM BY QM United States Patent O M METHOD OF MAKING COIL FORABSORPTION REFRIGERATION APPARATUS Bengt Reistad Reistad, Bromma,Sweden, assignor to Aktiebolaget Electrolux, Stockholm, Sweden, acorporation of Sweden Filed Mar. 27, 1964, Ser. No. 355,337 Claimspriority, application Sweden, Mar. 29, 1963, 3,597/ 63 4 Claims. (Cl.72217) My invention relates to a method of making a coil for absorptionrefrigeration apparatus. More particularly, the invention relates toevaporator and absorber coils for absorption refrigeration apparatus ofthe inert gas type.

It is an object of my invention to provide an improved coil of this typewhich includes straight portions and connecting bends having small radiiof curvature, whereby a maximum number of straight coil portions may beprovided in a space of a given size.

Another object of the invention is to provide an improved coil of thistype which includes two banks of straight portions spaced from oneanother and connecting bends having small radii of curvature, wherebythe space between the two banks of straight portions will be at aminimum.

A further object of my invention is to provide an improved method ofmaking a coil of this type in which spaced longitudinal regions ofstraight piping or tubing of cylindrical form are deformed to produceportions which are non-circular in cross-section and include a reentrantpart at a first side wall which functions as a support for the oppositesecond side wall when the noncircular portion is bent about the firstside wall to produce a bend in the coil.

The above and other objects and advantages of my invention will bebetter understood from the following description taken in connectionwith the accompanying drawing forming a part of this specification, andin which:

FIG. 1 is a view more or less diagrammatically illustrating anabsorption refrigeration apparatus of the inert gas type to which theinvention has been applied;

FIG. 2 is a fragmentary vertical sectional view of a refrigerator and anevaporator therefor which embodies the invention and is associated withrefrigeration apparatus like that shown in FIG. 1;

FIG. 3 is a horizontal sectional view taken at line 3-3 of FIG. 2 toillustrate the evaporator more clearly and also an absorber whichembodies the invention;

FIG. 4 is a fragmentary vertical sectional view taken at line 44 of FIG.2;

FIG. 5 is a fragmentary vertical sectional view taken at line 55 of FIG.3;

FIGS. 6 and 7 are diagrammatic views illustrating the manner in whichthe bends are formed in a bending machine; and

FIGS. 8 and 9 are vertical sectional views taken at lines 8-8 and 9-9,respectively, of FIG. 7.

In FIG. 1, I have shown absorption refrigeration apparatus of a uniformpressure type which is well known in the art and in which an inertpressure equalizing gas is employed. Such a refrigeration apparatuscomprises a generator or boiler 10 containing a refrigerant, such asammonia, in solution in a body of absorption liquid, such as water. Heatmay be supplied to the boiler 10 from a heating tube or flue 11thermally connected therewith, as by Welding. The heating tube 11 may beheated in any suitable manner, as by a liquid or gaseous fuel burner 12,for example, which is adapted to project its flame into the lower end ofthe tube.

The heat supplied to the boiler 10 and its contents expels refrigerantvapor out of solution, and the vapor thus 3,348,402 Patented Oct. 24,1967 generated flows through a conduit 14 to an air-cooled condenser 15in which it is condensed and liquefied. Liquid refrigerant flows fromcondenser 15 through a conduit 16 into an evaporator 17 in which itevaporates and diffuses into an inert pressure equalizing gas, such ashydrogen, which enters the upper part thereof through a conduit 18. Dueto evaporation of refrigerant fluid into inert gas, a refrigeratingeffect is produced and heat is abstracted from the surroundings.

The rich gas mixture of refrigerant vapor and inert gas formed inevaporator 17 flows from the lower part thereof through a conduit 19 andabsorber vessel 20 into the lower part of an absorber coil 21. Inabsorber coil 21 the rich gas mixture flows countercurrent to downwardlyflowing absorption liquid which enters through a conduit 22. Theabsorption liquid absorbs refrigerant vapor from inert gas, and inertgas weak in refrigerant flows from the upper part of absorber coil 21through conduit 18 into the upper part of cooling element 16.

The circulation of gas in the gas circuit just described is due to thedifference in specific Weight of the columns of gas rich and weak,respectively, in refrigerant vapor. Since the column of gas rich inrefrigerant vapor and flowing from the evaporator 17 to the absorbercoil 21 is heavier than the column of gas weak in refrigerant vapor andflowing from absorber coil 21 to the evaporator 17, a force is producedor developed within the apparatus for causing circulation of gas in themanner described.

Absorption solution flows downward through coil 21 into the absorbervessel 20, and such solution, which is enriched in refrigerant, passesfrom the vessel through a conduit 23 and an inner passage or pipe 24 ofliquid heat exchanger 25 into the lower end of a vapor lift pipe or tube26 which is in thermal exchange relation with the heating tube 11, as bywelding. Liquid is raised by vaporliquid lift action through pipe 26into the upper part of boiler 10. Refrigerant vapor expelled out ofsolution in boiler 16, together with refrigerant vapor entering throughpipe 26, flows upward from the boiler through the conduit 14 to thecondenser 15, as previously explained.

The outlet end of condenser 15 is connected by an upper extension ofconduit 16 and a conduit 27 to a part of the gas circuit, as to theupper part of conduit 19, for example, so that any inert gas which maypass through the condenser 14 can flow into the gas circuit. Theabsorption liquid from which refrigerant vapor has been expelled flowsfrom the boiler 10 through a connection 28, an outer pipe or passage 29of the liquid heat exchanger 25 and conduit 22 into the upper part ofthe absorber coil 21. The circulation of absorption solution in theliquid circuit just described is effected by raising of liquid throughpipe .26.

In order to effect heat exchange between inert gas which is weak inrefrigerant and flowing to the evaporator 17 through the conduit 18 andinert gas which is rich in refrigerant and flowing from the evaporator17 through the conduit 19, the conduits 18 and 19 may be heatconductively connected to one another at 30 in any suitable manner.Also, the conduit 16 through which liquid refrigerant flows from thecondenser 15 to the evaporator 17 may be heat conductively connected at31 to the conduit 19 through which inert gas rich in refrigerant flowsto the absorber vessel 20-, thereby cooling the liquid refrigerantbefore it is introduced into the evaporator 17.

While the evaporator 17 in FIG. 1 is diagrammatically shown in the formof a vertical looped coil, a practical form of such a cooling elementmay be an arrangement in which the looped coil is disposed substantiallyin a single horizontal plane across the space to be cooled. Such apractical embodiment is shown in FIGS. 2 and 3 in which parts similar tothose shown in FIG. 1 are designated by the same reference numerals.

The evaporator 17 in FIGS. 2 and 3 comprises a looped coil which isdisposed substantially in a single horizontal plane and adapted toextend from one lateral side wall 32 to the opposite lateral side wall32 of a thermally insulated storage compartment 33 of a refrigeratorcabinet 34 provided with a door 35 hinged at 36 to the front of thecabinet. The thermally insulated walls defining the storage compartment33' include a rear insulated with 37 having an opening and a removableenclosure member 38 therefor and through which the evaporator 17 isadapted to be inserted into the insulated interior of the cabinet 34.The parts of the conduits 18 and 19 heat conductively connected to oneanother at 30 and the part of the liquid refrigerant conduit 16 heatconductively connected to the conduit 19 at 31 may be disposed withinthe closure member 38 and retained therein within a body of insulation.

In FIGS. 2 and 3 the boiler 10, absorber vessel 20, absorber 21 andcondenser 15 are disposed in a vertically extending apparatus space 39at the rear of the refrigerator cabinet 34. The parts of the boiler areembedded in insulation retained within a shell 40, the heating tube 11projecting through openings in the top and bottom, respectively, of theshell. Upward circulation of air is induced by natural draft in thecompartment 39 which defines a vertically extending flue, and suchupward movement of air efi'ects cooling of the absorber coil 21 at onelevel and the condenser located at a higher level.

As shown in FIGS. 2 and 3, the evaporator 17 is heat conductivelyconnected in any suitable manner to the underside of a horizontallydisposed plate 41. The plate 41, which is positioned closely adjacent toand at the vicinity of the ceiling 42 of the storage compartment 33,extends substantially over the entire width of the storage compartment33 and from the rear insulated wall 37 to a region 43 at the open frontwhich is relatively close to the rear face of the door to divide thecompartment 33 into upper and lower spaces 33a and 33b, respectively.

The evaporator 17, which is adapted to be operated below the freezingtemperature of water, is employed to abstract heat from the plate 41which constitutes the bottom of the upper space 33a which functions asthe freezing section of the refrigerator. The plate 41 and evaporator 17in thermal exchange therewith also are employed to effect cooling of airin the lower space 33b of the storage compartment 33 which flows inthermal exchange relation therewith. Hence, the plate 41 has a limitedheat transfer surface which is employed to effect cooling of air in thebottom space 33b of the storage compartment 33.

The parts of the absorption refrigeration apparatus shown in FIGS. 2 and3 and just described, whose relative positions are substantially fixed,usually are formed of iron or steel when ammonia and water are employedas the refrigerant and liquid absorbent, respectively. Therefore, thepiping for the evaporator 17 and absorber 21, which are connected byconduits to other parts of the refrigeration apparatus and form aunitary part thereof, are formed of such ferrous metal having relativelythick walls. As best shown in FIG. 3, the looped coil forming theevaporator 17 includes straight sections 17a and connecting bends 17b;and the looped coil forming the absorber 21 includes straight sections21a and connecting bends 21b.

In accordance with my invention, in order to provide evaporator andabsorber coils having straight portions connected by bends having smallradii of curvature, the piping forming the bends of the coils isnon-circular in cross-section with a minor axis and longer major axiswhich is substantially parallel to the axes of the bends, whereby amaximum number of straight coil sections or portions may be disposed ina space of a given size. As shown in FIG. 4, the bends 17b of theevaporator coil 17 are formed of piping which is non-circular incrosssection and has the shape of the numeral eight with 4 top andbottom parts 17c of annular form and a narrow neck part 17dtherebetween.

As seen in FIG. 4, the bends 17b of the evaporator coil 17 havehorizontal minor axes and longer vertical major axes 17e-17e which areparallel to the axes of the radii of curvature of the bends. The narrowneck parts 17d of the bends 17b are formed by reentrant portions 17f and17g at the longer vertical side walls of the piping, the innerextremities of which contact and abut one another. Hence, the major axis17e-17e of each bend 17b extends substantially in the same direction asthe axis of the radius of curvature of the bend.

As seen inFIG. 5, the bends 21b of the absorber coil 21 also arenon-circular in cross-section and have the shape of the numeral eightwith top and bottom parts 21c and narrow connecting neck parts 21dtherebetween. The longer vertical major axes 21e21e of the bends 21b areparallel to the axes of the radii of curvature of the bends. Hence, themajor axis 21e-21e of each bend 21b extends substantially in the samedirection as the axis of the radius of curvature of the bend. Also, theneck parts 21d are formed by reentrant portions 21 and 21g at the longervertical sides of the piping, the inner extremities of which contact andabut one another. The straight portions 17a of the evaporator coil 17are of cylindrical form and have inner diameters substantially equal tothe distance between the inner surfaces of the opposing walls of thecoil 17 at the connecting bends 17b at the immediate vicinities of themajor axes 17c-17e thereof. Likewise, the straight portions 21a of theabsorber coil 21 are of cylindrical form and have inner diameterssubstantially equal to the distance between the inner surfaces of theopposing walls of the coil 21 at the connecting bends 21a at theimmediate vicinities of the major axes 21e- 21e thereof.

By providing evaporator and absorber coils 17 and 21 formed with bends17b and 21b of the kind just described and shown in FIGS. 4 and 5, agreater number of coil straight sections can be employed in a givenspace than otherwise would be possible. This is so because the bends 17band 21b can be formed with smaller radii of curvature than the bendsthat could be formed from the piping which is cylindrical incross-section and provide the straight sections of the coils. Byproviding the bends 17b for the evaporator coil 17 in FIG. 3, forexample, a maximum number of straight pipe sections 17a can be employedalongside one another in heat conductive relation with the underside oftheplate 41. In this way a longer path of flow for the liquidrefrigerant can be provided at the underside of the plate 41 whereby therefrigerating effect produced due to evaporation of refrigerant fluidinto inert gas is increased. 7

I make the evaporator and absorber coils 17 and 21 by deforming into theshape of the numeral eight longitudinally spaced regions of ferrouspiping which is cylindrical in cross-section. After straight lengths ofpiping are deformed at regions at which the bends of the piping are tobe formed, the piping is positioned in a suitable pipe bending machinehaving a pivot 44, a pair of backup rollers 45, and a roller 46 which ismounted for movement on an arm in any suitable manner (not shown) tobend the piping. The roller 46 is shown in one position in FIG. 6 aftera bend is partly made and in another position in FIG. 7 after the bendis completed.

As shown in FIG. 8, the roller 46 is formed with an outer peripheralwall 46a having the shape of the outer vertical side of the pipingagainst which it bears. However, the outer peripheral wall 44a of thepivot 44, which bears against the inner vertical side of the piping, isessentially straight, as shown in FIG. 9. Accordingly, after the bend isformed the roller 46 can be retracted from the position shown in FIG. 7and the bend just formed can be removed from the pivot 44 by a simplelifting movement.

As shown in FIGS. 7 and 8, the axis of the radius of curvature of thebend is parallel to the major axis 17e17e of the region of the pipingdeformed into the shape of the numeral eight. While the bend is beingformed, the reentrant portion 17 at the inner side wall of the pipingfunctions as a support against which the reentrant portion 17g at theouter side Wall of the piping bears. This enables the bends in theevaporator and absorber coils 17 and 21 to be formed by cold bendingwithout the necessity of heating the piping before or during the bendingoperation. By first deforming longitudinally spaced regions in suitableapparatus to provide piping sections having opposed reentrant portionsin the longer side walls thereof, the deformed regions offer lessresistance to bending than the piping of circular crosssection before itwas deformed.

When the deformed region of the piping is being bent, the outer sidewall thereof is subjected to tensile forces and the inner side wallthereof is subjected to compressive forces. The magnitude of the tensileand compressive forces developed in piping when it is being bent and theability of the piping to withstand these forces without localizedbuckling is dependent upon the ratio of the diameter of the piping tothe radius of curvature of the bend. By deforming the piping in themanner shown in FIGS. 4 and 5 at the regions at which the bends are tobe formed, the effective diameter of the piping is reduced for thebending operation without unduly decreasing the overall cross-sectionalarea of the piping at the bends.

In absorption refrigeration apparatus of the inert gas type a force isproduced within the apparatus for causing circulation of gas through andbetween the evaporator 17 and absorber 21, as explained above. In theevent the deforming of the piping by providing opposed reentrantportions at the longer side walls thereof reduces the overallcross-section of the piping to such an. extent that the circulation ofgas in the gas circuit will be impaired. it may be desirable to selectpiping for the evaporator and absorber coils of such size that, afterforming bends in the coils in the manner shown and described above, theoverall cross-sectional areas at the bends of the coils will besufliciently large not to impair operation of the refrigerationapparatus.

It will thus be seen that I have provided an improved evaporator andabsorber formed by coils having straight portions and connecting bendsand an inlet and outlet for inert gas at different elevations. Byproviding the reentrant portions at the opposing longer side walls ofthe piping with their inner extremities contacting and abutting oneanother, the inner side wall of the piping effectively functions tosupport the outer side Wall during the bending operation. Although thepiping of the evaporator coil 17 is deformed to provide the bends 17b,the height of the piping at the bends is not changed to such an extentthat it Will adversely affect the downward flow of liquid refrigerantthrough the coil by gravity.

By providing bends 21b for the absorber coil 21 having small radii ofcurvature in accordance with my invention the two banks of the straightsections 21a of the coil will be closer to one another so that the depthof the apparatus space 39 can be reduced. Moreover, by providing bends21b which not only have small radii of curvature but also are inclineddownward, the absorber coil 21 can be formed with straight sections 21awhich are essentially horizontal, whereby a greater number of straightpipe sections can be employed in an absorber coil of a given height thanin an absorber coil where the straight pipe sections and bends are bothinclined to the horizontal.

Although I have illustrated and described a particular embodiment of myinvention, I do not desire to be limited to the particular arrangementset forth, and I intend in the following claims to cover allmodifications which do not depart from the spirit and scope of myinvention.

I claim:

1. A method of making a coil for a gas circuit of absorptionrefrigeration apparatus which comprises first deforming a region of astraight piece of pipe which is cylindrical in cross-section and formedof ferrous metal to provide a pipe section at said region having a minoraxis and a longer major axis and a longitudinal reentrant portion in thewall thereof, and thereafter bending the pipe back upon itself to form abend at said region and straight pipe sections connected thereto Withthe major axis of said region extending substantially in the samedirection as the axis of the radius of curvature of the bend and thereentrant portion at the inside Wall of the bend and the inner diameterof each straight pipe section being substantially equal to the distancebetween the inner surfaces of the opposing Walls of said pipe section atthe bend at the immediate vicinity of the major axis thereof, thelongitudinal reentrant portion functioning to support the opposite outerside wall of the pipe at the bend while it is being formed.

2. A method of making a coil for a gas circuit of absorptionrefrigeration apparatus which comprises first deforming a region of astraight piece of pipe which is circular in cross-section and formed offerrous metal to provide a pipe section which is non-circular incross-section with a longitudinal reentrant portion in the wall thereofand has a minor axis passing through the reentrant portion and a longermajor axis transverse thereto, and thereafter bending the pipe back uponitself to form a bend at said region and straight pipe sectionsconnected thereto with the major axis of said region extendingsubstantially in the same direction as the axis of the radius ofcurvature of the bend and the reentrant portion at the inside wall ofthe bend and the inner diameter of each straight pipe section beingsubstantially equal to the distance between the inner surfaces of theopposing walls of said pipe section at the bend at the immediatevicinity of the major axis thereof, the longitudinal reentrant portionfunctioning to support the opposite outer side wall of the pipe at thebend while it is being deformed.

3. A method of making a coil for a gas circuit of absorptionrefrigeration apparatus which comprises first deforming a region of astraight piece of pipe which is circular in cross-section and formed offerrous metal to provide a pipe section which is non-circular incross-section with longitudinal reentrant portions in the wall atopposite sides thereof and has a minor axis passing through thereentrant portions and a longer major axis transverse thereto, andthereafter bending the pipe back upon itself to form a bend at saidregion and straight pipe sections connected thereto with the major axisof said region extending substantially in the same direction as the axisof the radius of curvature of the bend and one of the reentrant portionsat the inside wall of the bend and the inner diameter of each straightpipe section being substantially equal to the distance between the innersurfaces of the opposing walls of said pipe section at the bend at theimmediate vicinity of the major axis thereof, said one longitudinalreentrant portion contacting and bearing against the other of thelongitudinal reentrant portions at the outer side Wall of the pipe atthe bend and functioning to support the outer side wall of the pipe atthe bend while it is being formed.

4. A method of making a coil for a gas circuit of absorptionrefrigeration apparatus which comprises first deforming a region of astraight piece of pipe which is circular in cross-section and formed offerrous metal to provide a pipe section which in cross-section has theshape of the numeral eight having adjacent parts of annular form and acontracted neck part therebetween and has a minor axis and a longermajor axis transverse thereto passing through the contracted neck partand bisecting the parts of annular form, and thereafter bending the pipeback upon itself to form a bend at said region and straight pipesections connected thereto with the major axis of said region exetndingsubstantially in the same direction as the axis of the radius ofcurvature of the bend and one of the reentrant portions at the insidewall of the bend and the inner diameter of each straight pipe sectionbeing substantially equal to the distance between the inner surfaces ofthe opposing walls of said pipe section at the bend at the immediatevicinity of the major axis thereof, said one longitudinal reentrantportion contacting and bearing against the other of the longitudinalreentrant portions at the outer side wall of the pipe at the bend andfunctioning to support the outer side wall of the pipe at the bend whileit is being formed.

References Cited UNITED STATES PATENTS Thomas 62--515 Earl 165168 Draperet al 29157.6 Louthan 138-38 Kogel 62-490 Neeley 1532 10 CHARLES W.LANHAM, Primary Examiner.

ROBERT A. OLEARY, Examiner.

R. D. GREFE, Assistant Examiner.

1. A METHOD OF MAKING A COIL FOR A GAS CIRCUIT OF ABSORPTIONREFRIGERATION APPARATUS WHICH COMPRISES FIRST DEFORMING A REGION OF ASTRAIGHT PIECE OF PIPE WHICH IS CYLINDRICAL IN CROSS-SECTION AND FORMEDOF FERROUS METAL TO PROVIDE A PIPE SECTION AT SAID REGION HAVING A MINORAXIS AND A LONGER MAJOR AXIS AND A LONGITUDINAL REENTRANT PORTION IN THEWALL THEREOF, AND THEREAFTER BENDING THE PIPE BACK UPON ITSELF TO FORM ABEND AT SAID REGION AND STRAIGHT PIPE SECTIONS CONNECTED THERETO WITHTHE MAJOR AXIS OF SAID REGION EXTENDING SUBSTANTIALLY IN THE SAMEDIRECTION AS THE AXIS OF THE RADIUS OF CURVATURE OF THE BEND AND THEREENTRANT PORTION AT THE INSIDE WALL OF THE BEND AND THE INNER DIAMETEROF EACH STRAIGHT PIPE SECTION BEING SUBSTANTIALLY EQUAL TO THE DISTANCEBETWEEN THE INNER SURFACES OF THE OPPOSING WALLS OF SAID PIPE SECTION ATTHE BEND AT THE IMMEDIATE VICINITY OF THE MAJOR AXIS THEREOF, THELONGITUDINAL REENTRANT PORTION FUNCTIONING TO SUPPORT THE OPPOSITE OUTERSIDE WALL OF THE PIPE AT THE BEND WHILE IT IS BEING FORMED.